hwrng: core - use RCU and work_struct to fix race condition

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Summary

CVECVE-2026-45949
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-05-27 14:17:11 UTC
Updated2026-05-27 14:48:03 UTC
DescriptionIn the Linux kernel, the following vulnerability has been resolved: hwrng: core - use RCU and work_struct to fix race condition Currently, hwrng_fill is not cleared until the hwrng_fillfn() thread exits. Since hwrng_unregister() reads hwrng_fill outside the rng_mutex lock, a concurrent hwrng_unregister() may call kthread_stop() again on the same task. Additionally, if hwrng_unregister() is called immediately after hwrng_register(), the stopped thread may have never been executed. Thus, hwrng_fill remains dirty even after hwrng_unregister() returns. In this case, subsequent calls to hwrng_register() will fail to start new threads, and hwrng_unregister() will call kthread_stop() on the same freed task. In both cases, a use-after-free occurs: refcount_t: addition on 0; use-after-free. WARNING: ... at lib/refcount.c:25 refcount_warn_saturate+0xec/0x1c0 Call Trace: kthread_stop+0x181/0x360 hwrng_unregister+0x288/0x380 virtrng_remove+0xe3/0x200 This patch fixes the race by protecting the global hwrng_fill pointer inside the rng_mutex lock, so that hwrng_fillfn() thread is stopped only once, and calls to kthread_run() and kthread_stop() are serialized with the lock held. To avoid deadlock in hwrng_fillfn() while being stopped with the lock held, we convert current_rng to RCU, so that get_current_rng() can read current_rng without holding the lock. To remove the lock from put_rng(), we also delay the actual cleanup into a work_struct. Since get_current_rng() no longer returns ERR_PTR values, the IS_ERR() checks are removed from its callers. With hwrng_fill protected by the rng_mutex lock, hwrng_fillfn() can no longer clear hwrng_fill itself. Therefore, if hwrng_fillfn() returns directly after current_rng is dropped, kthread_stop() would be called on a freed task_struct later. To fix this, hwrng_fillfn() calls schedule() now to keep the task alive until being stopped. The kthread_stop() call is also moved from hwrng_unregister() to drop_current_rng(), ensuring kthread_stop() is called on all possible paths where current_rng becomes NULL, so that the thread would not wait forever.

Risk And Classification

EPSS: 0.000180000 probability, percentile 0.049330000 (date 2026-05-30)

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected be4000bc4644d027c519b6361f5ae3bbfc52c347 d5b7730f06994499632026c30e38e0317c4569e2 git Not specified
CNA Linux Linux affected be4000bc4644d027c519b6361f5ae3bbfc52c347 dcf416eb88eafe1e3c0f920a14bdffd10bc4d259 git Not specified
CNA Linux Linux affected be4000bc4644d027c519b6361f5ae3bbfc52c347 ad38f2cdfef9a2f2899c30cad269baec5bfd4a5d git Not specified
CNA Linux Linux affected be4000bc4644d027c519b6361f5ae3bbfc52c347 cc2f39d6ac48e6e3cb2d6240bc0d6df839dd0828 git Not specified
CNA Linux Linux affected 3.17 Not specified
CNA Linux Linux unaffected 3.17 semver Not specified
CNA Linux Linux unaffected 6.12.75 6.12.* semver Not specified
CNA Linux Linux unaffected 6.18.14 6.18.* semver Not specified
CNA Linux Linux unaffected 6.19.4 6.19.* semver Not specified
CNA Linux Linux unaffected 7.0 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/cc2f39d6ac48e6e3cb2d6240bc0d6df839dd0828 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/d5b7730f06994499632026c30e38e0317c4569e2 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/dcf416eb88eafe1e3c0f920a14bdffd10bc4d259 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/ad38f2cdfef9a2f2899c30cad269baec5bfd4a5d 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
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